Wax emulsions

ABSTRACT

THE MANUFACTURE OF A ANIONIC WAX SIZE EMULSION CONCENTRATE WHICH CONTAINS AN ANIONIC COLLOID PROTECTOR BY ADDING A SMALL AMOUNT OF AN AQUEOUS SOLUTION OF A WATER: SOLUBLE SALT OG A POLYVALENT METAL WHICH FORMS AN INSOLUBLLE HYDROXIDE WITHIN THE RANGE OF 2 TO 10, BEFORE DURING OR AFTER THE ENULSIFICATION STEP, AND THEN PRECIPITATING AT LEAST A PART OF THE METAL OF THE ADDED SALT AS A SALT WITH SAID PROTECTIVE COLLOID.

United States Patent 3,709,708 WAX EMULSIONS Edward Strazdins, Stamford, Conn, assignor to American Cyanamid Company, Stamford, Conn. No Drawing. Continuation-impart of applications Ser. No.

500,242, Oct. 21, 1965, and Ser. No. 667,373, Sept. 13,

1967. This application Feb. 16, 1970, Ser. No. 11,779

Int. Cl. C0811 9/10 US. Cl. 106-216 10 Claims ABSTRACT 0F THE DISCLOSURE This is a continuation-in-part of my copending applications, Ser. Nos. 500,242, and 667,373 respectively filed on Oct. 21, 1965, and Sept. 13, 1967, and now abandoned.

The present invention relates to wax size. More particularly it relates to anionic wax size emulsion concentrates of improved mechanical stability and to processes for the manufacture thereof.

In this art, the term emulsion designates wax size both at the temperature at which the wax therein is liquid and at the temperature where the wax is a solid, and the term concentrate is used to indicate that the size is at least about 40% wax by weight.

Anionic wax size emulsion concentrates as commercially sold are emulsions of cream-like viscosity consisting essentially of microspheroidal particles of normally solid hydrocarbon wax dispersed at about 40%- 60% solids by weight in an aqueous medium consisting essentially of water, an anionic emulsifying agent for the wax, and an anionic polysaccharide as protective colloid for the Wax. The wax is present in highly particulate state. The particles are at least in the semi-colloidal state, i.e., they are in therange of 0.5a to 5p; so that they are substantially non-creaming in aqueous dispersion. Preferably the particles are of the smaller dimension. These emulsions are used on a large scale for the manufacture of paper and paper board, and are particularly valuable in the manufacture of water-resistant particle board.

Before use, the size is customarily diluted to l%-5% solids and the resulting watery dispersion is pumped into the papermaking fibrous suspension at a suitable location in the papermaking machine, for example, at the fan pump.

Anionic wax size emulsion concentrates suffer from the disadvantage in that they are mechanically unstable. When these concentrates are subjected to mechanical working, for example by passage through a centrifugal pump, the wax microspheres tend to aggregate and to lose their colloidal or semicolloidal character. As a result, the water-resistance which is imparted by the size when the size is used in paper or particle board manufacture is decreased.

The discovery has now been made that the mechanical stability of anionic wax size emulsion concentrates is increased when there is added a small amount of a soluble salt of polyvalent metal which forms an insoluble hydroxide at a pH within the range of 2 to 10, and at least a part of the metal content of said salt is precipitated as a salt with said protective colloid. As a result, the

3,709,708 Patented Jan. 9, 1973 ICC concentrate can be subjected to the agitation incident to pumping more often and at higher pressures than would otherwise be the case without causing the particles of the wax in the emulsion concentrate to coalesce or aggregate. The concentrate can thus be pumped to greater distances without harm.

In the process, the metal content of the added salt is changed to hydroxylated metal ions (or complex of hydroxylated metal ions) of unknown composition (hereinafter for convenience termed insoluble hydrous oxide) which precipitates as a salt of the anionic protective colloid forming a complex therewith. The identity of the insoluble hydrous oxide complex has not been ascertained, and it is not known whether this complex is adsorbed by the wax microspheres or whether it remains discretely dispersed in the aqueous phase of the emulsion. The invention results from our discovery that the presence of this complex in the emulsion inhibits the tendency of the wax microspheres to coalesce, thereby enhancing the mechanical stability of the emulsion.

Suitable salts which may be added for the purpose described above are soluble salts of aluminum, bismuth, chromium, cerium, copper, iron, zinc and zirconium and mixtures thereof. These salts are soluble in dilute acid and form insoluble hydrous oxides in the following pH ranges:

pH of hydrous pH values in the lower parts of these ranges (hereinafter termed in each instance the hydrolysis range) are preferred as in these parts of the range (hydroxy ion) formation predominates over formation of the respective full hydroxides.

Best results at lowest cost have been obtained with aluminum and zinc salts, which for this reason are preferred. Salts of amphoteric metals are suitable. Additional salts are shown in Moellers Inorganic Chemistry, pp. 501-503 (John Wiley & Co., New York, NY. 1952).

The amphoteric metals in this group may be added as their acidic compounds with bases to emulsions having an alkaline pH. Thus, if desired, sodium aluminate, sodium bismuthate, sodium zincate, etc., may be added and the metal content thereof then converted to effective insoluble hydrous oxide form by lowering the pH of the emulsions. For convenience these materials are herein included within the term salt.

The amount of salt added should be sufficient to provide between about 0.001% and 1% of metal, based on the total weight of the size concentrate, and need not be greater than that which imparts the desired amount of mechanical stability to the emulsion. Suitable amounts within the range mentioned can readily be determined by laboratory trails as is shown in detail below. A larger amount may be added, but confers no additional mechanical stability or actually renders the size less stable to mechanical forces. I prefer to have about 0.1%-0.5% of metal present based on the total weight of the size concentrate as in this range a good improvement in stability is effected without danger of adverse effects from the presence of too much of metal. Best stabilization appears to occur when the insoluble hydrous oxide formed by hydrolysis of the added salt is stoichiometrically equivalent to the anionic protective colloid.

The size concentrates of the present invention in addition may contain minor amounts of such materials as are customarily present in commercial size concentrates, for example, an inhibitor of the growth of bacteria, fungi, etc. (for example, sodium pentachlorophenol or an anionic amineformaldehyde condensate); a pigment (for example, titanium dioxide white, carbon black, or ultramarine blue); starch; an anionic or non-ionic dye; or a perfume.

Wax size emulsion concentrates are customarily prepared by slowly adding with rapid agitation a normally solid hydrocarbon wax in molten state to about an equal weight of hot Water containing a dispersing agent and a polysaccharide colloid protector (protective colloid) for the wax, homogenizing the crude emulsion thus formed to produce a colloidal or semi-colloidal emulsion of wax droplets in the aqueous medium, and rapidly cooling the emulsion to below the solidfication point of the wax to inhibit aggregation of the particulate droplets. The concentration of wax in the emulsion is usually at the maximum point at which. the emulsion is of pumpable viscosity.

A non-ionic emulsifier may be present as assistant for the anionic emulsifier. Further details regarding wax size are shown at p. 1144 if. of Pulp and Paper, vol. II (2nd ed.) by Casey.

Wax size emulsion concentrates of the present invention are preferably prepared by introducing an aqueous solution of a soluble salt of the desired polyvalent metal at any convenient point in the size-making process, the pH of the emulsion being adjusted (if necessary) before, during or after the addition to the value at which the metal content of the salt forms a hydroxide.

Thus, the salt may be dissolved in the starting aqueous medium, i.e., the aqueous medium used for the emulsification, before or after addition of the emulsifying agent or the colloid protector. In the case of normal salts such as aluminum sulfate wherein the metal is the cation, the aqueous medium has an acidic pH below the range shown above for the particular metal and in the case of salts wherein the polyvalent metal i part of the anion the aqueous medium has an alkaline pH. At a later point, subsequent to emulsification of the wax, the pH of the size concentrate is adjusted to a value at which the polyvalent metal forms a full hydroxide or (preferably) a hydroxy ion or a hydroxy ion complex, upon which a metathesis occurs which results in formation of a salt of the polyvalent metal as a hydrous ion with the protective colloid.

The salt may be also introduced as a component of the solution of the dispersing agent or as a component of the solution of the polysaccharide gum, so long as sufiicient water is present and the pH is appropriate to prevent formation of a precipitate or gel.

The salts added may have any convenient composition, and include zinc chloride. zinc picrate, zinc nitrate, zinc acetate, aluminum chloride, aluminum nitrate, aluminum sulfate, ferrous sulfate, chromic chloride, ceric sulfate, chromic sulfate, cupric chloride, and cupric sulfate. If desired, the salts can be added as solids, in crushed or powdered form, but it is more convenient to add them dissolved in aqueous medium of appropriate pH. In the final size concentrate at least a part of the polyvalent metal i present as a component of the dispersing agent, the polysaccharide gum, or both. Not all of the added salt need be present in such manner; some is evidently present in unreacted state in the aqueous phase. This amount is small and is tolerated well by the size.

Anionic dispersing agents whichv can be used for the manufacture of wax size concentrates include sodium formaldehyde-naphthalene sulfonate (Tanak A), sodium lignosulfonate, and sodium lauryl sulfate (Duponol C). Anionic polysaccharides which can be used as protective colloids in these compositions include gum arabic, gum ghatti, gum shiraz, gum guar, cooked potato starch, enzyme converted starches, and hydrolyzed gum karaya. They are hydrophilic and water-dispersible or watersoluble.

The size concentrates of the present invention find practical use in the same manner as previously known size concentrates. The presence of the small amount of reacted polyvalent metal in the size is not apparent to the user of the size or to the consumer of the paper, and does not require any change in application procedures. Before use, the size concentrate is diluted with water to a convenient solids content (typically 0.1% to 1%) and is applied to paper in a size press or by spray, or to particle board by spray or roller coater. The presence of the reacted metal does not cause the wax to decrease in its sizing power, and generally the size possesses superior sizing properties because the wax particles are in unaggregated or les aggregated state so that they have better covering power per unit weight.

The invention is further illustrated by the examples which follow. These examples are preferred embodiments of the invention and are not to be construed in limitation thereof.

EXAMPLE 1 The following illustrates the preparation of a preferred wax size emulsion concentrate according to the present invention, wherein the polyvalent metal salt is added after the emulsification step has been performed.

0.70 lb. of dry gum ghatti (as the calcium salt) is dissolved in 10 lb. of water at 180 F. in a tank equipped with thermometer and high-speed stirrer. To the solution is added with rapid agitation 44 lbs. of water at 180 F., followed by 2.0 lbs. of sodium lignosulfonate (Marasperse N) and 41.8 lbs. of molten slack wax (a petroleum hydrocarbon paper-sizing wax having a melting point of 130 F.). The foam which forms is allowed to subside and 0.04 lb. of 50% aqueous sodium hydroxide solution is added. The crude emulsion thus formed is homogenized. The emulsified droplets range from 0.5a to 5p in diameter, and roughly 75% are l to 2 in diameter. The product is rapidly cooled to 115 F. To half of the resulting size concentrate (portion A) is added with stirring 8 oz. of 20% aqueous zinc sulfate solution at its natural acidic pH of about 3. The other half (portion B) is left untreated. Both portions contain about 45% solids by weight. The pH of each portion is adjusted to 7.

The size concentrates are tested to determine their mechanical stability by being pumped for 10 minutes through a laboratory piston pump working against a lbs/in. discharge pressure with 100% recirculation, after which a sample of each of the concentrates is placed in a laboratory graduate. After 48 hours of standing the height of any cream layer present is noted as a percent of the height of the column), and a sample of each is examined by microscope to determine the amount of any aggregated wax particles present.

The comparative efiiciency of these samples as sizes is then determined by impregnating ZOO-lb. (25" x 40/ 500 ream) water-leaf sheets with the concentrates diluted to 1% with water, drying the paper for 2 minutes on a drum drier having a drum temperature of 240 F., and determining the sizing of the sheets.

Results are as follows:

Percent Aggregated Percent Sizing ZnSOi wax particles cream. (secs) 3 Portion A 0.2 None None 1,350 B None Many 10 925 In the process, the addition of the sodium hydroxide is optional in that it causes only a minor improvement. Nearly the same results are achieved when it is omitted.

EXAMPLE 2 The procedure for the preparation of portion B of Example 1 is repeated except that 0.5 lb. of sodium pentachlorophenol is added with the water as spoilage inhibitor. Substantially the same product is obtained.

EXAMPLE 3 Aggregated Percent wax Percent alum. particles cream Portion:

A 0.4 None None B None Many 1 Based on total weight of size.

EXAMPLE 4 The procedure of Example 1 is repeated except that the zinc sulfate solution is replaced by an equal amount of ceric sulfate solution having a pH of 3. A similar improvement is obtained.

EXAMPLE 5 The procedure of Example 1 is repeated except that an equal amount of ferrous sulfate is used in place of the zinc sulfate and the pH is adjusted to 4.5. A similar improvement is obtained.

EXAMPLE 6 The following illustrates the process of the present invention wherein the salt added is an aluminum salt and the metal content thereof precipitated prior to addition of the wax.

To 270 cc. of water at 160 F. containing 3.5 g. of gum ghatti in a Waring Blendor is added 10 g. of sodium lignosulfonate followed by 4.0 g. of a hot solution of aluminum sulfate at pH 2. The pH of the solution is then raised to 5.5 forming hydroxyaluminum ions which react with the gum and the sodium lignosulfonate. There is then added 210 g. of molten slack wax at 225 F. while the blendor is operating at high speed. Agitation at maximum speed is continued for two minutes, and the emulsion is then cooled in ice.

The resulting dispersion when tested by the method of claim 6 possesses better stability than a dispersion prepared in the same manner without addition of aluminum sulfate.

EXAMPLE 7 The following illustrates the process of the present invention wherein the polyvalent metal salt is a cerium compound.

To 265 g. of a solution of 3.5 g. of gum ghatti in hot water are added with stirring 0.5 g. of pentachlorophenol (Dowicide G) as preservative, 5.0 g. of sodium lignosulfonate as dispersant, and the solution is brought to 190 F. To the above solution with rapid agitation in a Waring Blendor is slowly added 235 g. of a highly refined parafiin wax having a melting point of about 135 F. (commercially known as F wax) at 200 F. Agitation is continued for three minutes. The resulting smooth creamy emulsion is rapidly cooled to 20 C. in ice. Two 250-g. portions of the resulting dispersion are removed.

To portion (portion A) at room temperature is added 37.4 g. of a freshly-prepared 2% by weight solution of ceric ammonium nitrate in water with gentle but 6 effective mixing (by spatula). The pH of the emulsion is adjusted to 4.5 by addition of sodium hydroxide solution and the weight is adjusted to 290 g. by addition of water. The resulting emulsion contains 40.5% wax solids by weight.

To the other (portion B) at room temperature is added 37.4 g. of Water with similar stirring and the emulsion is adjusted to pH 4.5 and 290' g. weight as in the case of portion B.

The comparative stabilities of the two emulsions are determined by the wet rub test, wherein a drop of the emulsion under test is placed on the dry palm of a hand, and the emulsion is rubbed with the index finger of the other hand until the emulsion breaks. The number of strokes needed to break the emulsion are indicative of the stability of the emulsion.

Results are as follows.

Finger strokes needed Sample: to break emulsion A 15 The results show that emulsion A is substantially more stable than emulsion B.

EXAMPLE 8 The following illustrates the process of the present invention by a method wherein the stabilizing component is formed in advance of the emulsification step.

To a solution of 3.5 g. of gum ghatti in 0.5 liter of hot F.) water in a Waring Blendor are added with stirring 75 g. of a freshly-prepared 2% solution of ceric ammonium nitrate in water. The pH- of the emulsion is adjusted to 4.5 causing formation of a cerium complex. There is then added 5 g. of sodium lignosulfonate as emulsifier; and then with rapid agitation 450 g. of highly refined paraffin wax (F wax) at 200 F. Agitation is continued until a smooth and creamy emulsion is obtained which is rapidly chilled to room temperature and diluted with water to 40% solids.

The size is substantially as effective as the size of Example 7.

I claim:

1. In the manufacture of an anionic wax size concentrate, wherein a normally solid hydrocarbon wax is emulsified in molten state in about an equal weight of aqueous medium containing an amonic dispersing agent for said wax and an anionic polysaccharide protective colloid for the wax microspheres which form, and the resulting emulsion is cooled below the solidification point of said Wax: the improvement which comprises the steps of (1) adding a small amount (in the range of 0.001% to 1% of metal based on the weight of said emulsion) of a soluble salt of a polyvalent metal which forms an insoluble hydrous oxide within the pH range of 2 to 10, and (2) precipitating at least a part of said metal as an insoluble hydrous oxide metal salt of said protective colloid by pH adjustment from a value outside of, to a value within the range of, 2 to 10, thereby forming a stabilizer which inhibits coalescence of said microspheres.

2. A process according to claim 1 wherein said soluble salt is a zinc salt.

3. A process according to claim 1 wherein said soluble salt is an aluminum salt.

4. A process according to claim 1 wherein the weight of said soluble salt is between 0.1% and 0.5% of the weight of said concentrate.

5. A process according to claim 1 wherein said soluble salt is added to said aqueous medium and at least part of the metal content thereof is precipitated before said wax is emulsified.

6. A process according to claim 1 wherein said soluble salt is added and at least part of the metal content thereof is precipitated after said wax has been emulsified.

7. A process according to claim 1 wherein said soluble salt is added after said emulsion has been cooled.

8. A process according to claim 1 wherein the pH of said aqueous medium when said soluble salt is added is sufficiently low that the metal content of said salt does not precipitate, and after said wax has been emulsified the pH of said aqueous medium is raised to a point at which said metal content precipitates.

9. An anionic wax size emulsion concentrate consisting essentially of colloidal wax microspheres uniformly dispersed in an aqueous medium having a uniformly distributed content of an insoluble hydrous oxide polyvalent metal salt of an anionic polysaccharide protective colloid as agent inhibiting aggregation of said microspheres, said metal being a metal which forms an insoluble hydrous oxide within the pH range of 2 to 10; said concentrate having a pH in the range of 2 to 10 at which said metal is present as an insoluble hydrous oxide; the weight of metal in said salt being between about 0.001% and 1% of the weight of said concentrate.

UNITED STATES PATENTS 2,173,243 9/1939 Young 117135.5 2,769,724 11/1956 Studenic 106-27l 2,711,378 6/1955 Holzinger 106271 2,402,351 6/1946 Smith et al. 106271 OTHER REFERENCES Bennett: Commercial Wax, p. 552 (1956).

THEODORE MORRIS, Primary Examiner U.S. Cl. X.R. 

